1. Field of the Invention
The present invention relates to dielectric ceramics suited for electrostatic chucks used to fix semiconductor wafers, correct flatness thereof or carry them in etching apparatus, CVD apparatus, electron beam exposure apparatus, light exposure apparatus, etc.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 94953/1987 discloses an electrostatic chuck prepared by firing alumina containing a certain transition metal oxide, in a reducing atmosphere.
The above electrostatic chuck, however, has a dielectric constant .epsilon. of from 9 to 10 at best, and requires application of a high voltage (about 400 V) in producing a given attracting force. Hence, it has been desired to provide dielectric ceramics for electrostatic chucks that have a higher dielectric constant and can produce a given attracting force with application of a lower voltage.
If the sole objective is to increase the dielectric constant, dielectric materials such as BaTiO.sub.3 may be used. However, materials for this kind all have a smaller mechanical strength than alumina, disadvantageously.